The invention generally relates to networks and, more particularly, the invention relates to reducing the effect of delay on a transmitted document.
Due to increasing telephone usage charges, it has become increasingly common for facsimile documents to be transmitted (i.e., xe2x80x9cfaxedxe2x80x9d) from a sending facsimile machine (xe2x80x9cfax machinexe2x80x9d) to a receiving fax machine via the Internet. Since fax documents are transmitted and received at a preselected, substantially constant rate (e.g., 28.8 kilobytes per second), use of the Internet for faxing documents introduces data delays that can corrupt the document data received by the receiving fax machine.
The art has responded to this problem by buffering data packets utilized to transport a faxed document across the Internet. This data is stored in no specific manner relative to the format of the actual document. Once in a buffer, the packets can be retrieved and forwarded to the receiving fax at a more consistent data rate. Problems arise with this solution, however, when the buffer is full. More particularly, when the buffer is full, incoming data packets can be dropped, thus requiring retransmission of the entire document. In a similar manner, problems also can arise when too few packets are in the buffer (i.e., many of the data packets transporting the document may have been delayed within the Internet and, consequently, not yet received by the buffer). Specifically, the buffer may not have enough data to transmit to the receiving fax at a given preselected data rate required by a given transmission. Accordingly, since the receiving fax is configured to receive the document data at the given preselected rate, then receipt of such data at a slower data rate can corrupt the faxed document.
In accordance with one aspect of the invention, a method and apparatus for transmitting a document across a network from a transmitting device to a receiving device reconstructs the document and stores the reconstructed document in a buffer. Specifically, the document is received from a packet based portion of the network as data packets. Data lines that comprise the document then are reconstructed from the received document data packets. The reconstructed data lines then are stored in the buffer, and retrieved at a substantially constant rate from the buffer as necessary. The reconstructed data lines then are transmitted to the receiving device across the network at about the substantially constant rate. In preferred embodiments, the document is transmitted from the transmitting device at the substantially constant rate.
In some embodiments, the receiving device is configured to receive the document at the substantially constant rate. The transmitting device and receiving device may be facsimile machines. The reconstructed lines may be transmitted to the receiving device via a public telephone network. The buffer may be coupled to a gateway that translates data between a packet based format and an analog format. The data lines may comprise scan lines of a facsimile document.
It may be determined if the total amount of data in the buffer is less than a minimum amount of data. If so, then additional data may be added to at least one reconstructed data line prior to transmitting it toward the receiving device. Conversely, instead of adding such additional data, at least one of the data lines in the buffer may be copied to produce at least one copied data line that can be transmitted to the receiving device. If the total amount of data in the buffer is greater than a maximum amount of data, then at least one data line may be deleted from the buffer prior to transmission to the receiving device, thus freeing memory in the buffer. The deleted data lines may be a preselected pattern of data lines. In other embodiments, data lines retrieved from the buffer may be converted into an analog data line signal that is transmitted along an analog portion of the network.
In accord with another aspect of the invention, an apparatus and method of controlling the effect of delay on a document transmitted across a network also stores data representing the document in a buffer. To that end, the document is received as document data packets from a packet based portion of the network, and then stored in the buffer. The total amount of data is monitored in the buffer to determine if the total amount of such data is less than a minimum amount of data. If below such minimum, then document data is transmitted across the network toward a receiving device. The transmitted document data includes the document and additional data associated with data lines of the document.
In accord with other aspects of the invention, an apparatus and method of controlling the effect of delay on a document transmitted across a network also buffers the document data. Specifically, document data packets utilized to transport the document are received from a packet based portion of the network, and then stored in the buffer. The stored data is changed in the buffer to produce changed document data if the total amount of data stored in the buffer is outside a preselected size range having maximum and minimum sizes. The changed document data is transmitted across the network toward a receiving network device.